Recently, as the resolution of a solid-state imaging element such as a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor becomes higher, a demand for an information device including an imaging function such as a digital still camera, a digital video camera, a cellular phone, and a personal digital assistant (PDA) is rapidly increasing. In the meantime, the information device having an imaging function as described above is referred to as an imaging device.
However, a focus control method which focuses on a main subject includes a contrast auto focus (AF) method and a phase difference AF method. Since the phase difference AF method may detect a focusing position with high precision at a high speed as compared with the contrast AF method, the phase difference AF method is widely employed in various imaging devices (see, for example, Patent Literature L).
In the phase difference AF method, generally, a phase difference (a deviated amount of an image) is detected by performing a correlation operation using a signal output from a photoelectric converting element for phase difference detection in a fixed area of the solid-state imaging element. However, when a region where a signal for phase difference detection is obtained is fixed, if a contrast of a subject is low, a phase difference may not be precisely detected.
Therefore, Patent Literature 1 discloses a method that broadens a region where a signal for phase difference detection is obtained to improve precision of phase difference detection when a contrast of a subject is low.
Specifically, Patent Literature 1 also discloses a method which, when a first focus is detected, performs correlation operation by setting a pitch of a signal for phase difference detection which is used for the correlation operation to be half a pixel pitch of the photoelectric converting element and roughly adjusts a focus by detecting a phase difference with low precision and thereafter, performs the correlation operation by setting the pitch of the signal for phase difference detection which is used for the correlation operation to be equal to the pixel pitch of the photoelectric converting element to detect the phase difference with high precision.